You can see with the rule book book and army book that it was lacking, so how about they create a forum for dedicated members to help create a vision. Have a vote/contribute/fan fiction thing going on.
I personally think that the pages in the rule book were too white, the text was to microsoft word, and there was no grit. Sure there was informatoin about the races and history, but most cut and pasted from the rpg book. It should be darker. The MI should have more of a feel of being slowly enroiached and pushed back over their history, but still be gung ho and propaganda fascist about it, with more cover ups. It would be a stark contrast to 40K where 'we are doomed but too afraid not to kill ourselves in case they kill our families', and the actualy standard human military have a pair of balls, unlike the imperial guard. You read the novels and they just peg it after something bad happens.
The arachnids should be more dark and sinister with a hidden intelligence and emnity towards humans, like the brain bug controlled humans talking in Starship troopers 2 (Iknow, *sigh*, I am referring to the sequel...). I feel that the CGI ones were more like this too. Hell, maybe they could even have an exclusive brain bug controlled symbiote race who do their bidding (kind of like Drahk and their keepres in babylon 5).
With skinnies, make them more aggro and alien. MGP already went out there with making the elite guard units look like predators with the dread and armour, I say keep th pulp sci fi stuff but make the faces morescary visious ugly and give them more evil and dark paint jobs. Might as well finish the job and turn them into hard asses like predators, but aggressive in a sort of klingong way. Maybe create a new unit of guard from a brute world, bulkier and tougher, with big miinies, like balck orcs

rcs as brute guard:guard.
From what I have heard about some races planned, like one that is like the strogg and the other like psychics, they could all be made dark, but not in a gothic 40K way, but a WW2 where verything goes to hell way but people keep trying for their own sake, not the 40K 'you're a heretic if you don't' way.